Histone Deacetylase Inhibitors as Multitarget Ligands: New Players in Alzheimer's Disease Drug Discovery?

Hydrazides as Inhibitors of Histone Deacetylases

In this Perspective, we have brought together available biological evidence on hydrazides as histone deacetylase inhibitors (HDACis) and as a distinct type of Zn-binding group (ZBG) to be reviewed for the first time in the literature. N-Alkyl hydrazides have transformed the field, providing innovative and practical chemical tools for selective and effective inhibition of specific histone deacetylase (HDAC) enzymes, in addition to the usual hydroxamic acid and o-aminoanilide ZBG-bearing HDACis. This has enabled efficient targeting of neurodegenerative diseases such as Alzheimer's disease, cancer, cardiovascular diseases, and protozoal pathologies.

Rethinking neurodegenerative diseases: neurometabolic concept linking lipid oxidation to diseases in the central nervous system

ABSTRACT

Currently, there is a lack of effective medicines capable of halting or reversing the progression of neurodegenerative disorders, including amyotrophic lateral sclerosis, Parkinson's disease, multiple sclerosis, or Alzheimer's disease. Given the unmet medical need, it is necessary to reevaluate the existing paradigms of how to target these diseases. When considering neurodegenerative diseases from a systemic neurometabolic perspective, it becomes possible to explain the shared pathological features. This innovative approach presented in this paper draws upon extensive research conducted by the authors and researchers worldwide. In this review, we highlight the importance of metabolic mitochondrial dysfunction in the context of neurodegenerative diseases. We provide an overview of the risk factors associated with developing neurodegenerative disorders, including genetic, epigenetic, and environmental factors. Additionally, we examine pathological mechanisms implicated in these diseases such as oxidative stress, accumulation of misfolded proteins, inflammation, demyelination, death of neurons, insulin resistance, dysbiosis, and neurotransmitter disturbances. Finally, we outline a proposal for the restoration of mitochondrial metabolism, a crucial aspect that may hold the key to facilitating curative therapeutic interventions for neurodegenerative disorders in forthcoming advancements.

Restoring the epigenome in Alzheimer's disease: advancing HDAC inhibitors as therapeutic agents

Current treatment options for Alzheimer's disease (AD) focus on symptom relief rather than halting disease progression. In this context, targeting histone deacetylation emerges as a promising therapeutic alternative. Dysregulation of histone deacetylase (HDAC) activity is present in AD, contributing to cognitive decline. Pharmacological HDAC inhibition has shown benefits in preclinical models, namely reduced amyloid beta plaque formation, lower phosphorylation and aggregation of tau protein, greater microtubule stability, less neuroinflammation, and improved metabolic homeostasis and cell survival. Nonetheless, clinical trials evidenced limitations such as insufficient selectivity or blood-brain barrier penetration. Hence, future innovative strategies are required to enhance their efficacy/safety.

Integrating a quinone substructure into histone deacetylase inhibitors to cope with Alzheimer's disease and cancer

Alzheimer's disease (AD) and cancer are among the most devastating diseases of the 21st century. Although the clinical manifestations are different and the cellular mechanisms underlying the pathologies are opposite, there are different classes of molecules that are effective in both diseases, such as quinone-based compounds and histone deacetylase inhibitors (HDACIs). Herein, we investigate the biological effects of a series of compounds built to exploit the beneficial effects of quinones and histone deacetylase inhibition (compounds 1-8). Among the different compounds, compound 6 turned out to be a potent cytotoxic agent in SH-SY5Y cancer cell line, with a half maximal inhibitory concentration (IC50) value lower than vorinostat and a pro-apoptotic activity. On the other hand, compound 8 was nontoxic up to the concentration of 100 μM and was highly effective in stimulating the proliferation of neural precursor cells (NPCs), as well as inducing differentiation into neurons, at low micromolar concentrations. In particular, it was able to induce NPC differentiation solely towards a neuronal-specific phenotype, without affecting glial cells commitment.

First in Class Dual Non-ATP-Competitive Glycogen Synthase Kinase 3β/Histone Deacetylase Inhibitors as a Potential Therapeutic to Treat Alzheimer's Disease

Despite recent FDA approvals, Alzheimer's disease (AD) still represents an unmet medical need. Among the different available therapeutic approaches, the development of multitarget molecules represents one of the most widely pursued. In this work, we present a second generation of dual ligands directed toward highly networked targets that are deeply involved in the development of the disease, namely, Histone Deacetylases (HDACs) and Glycogen Synthase Kinase 3β (GSK-3β). The synthesized compounds are highly potent GSK-3β, HDAC2, and HDAC6 inhibitors with IC50 values in the nanomolar range of concentrations. Among them, compound 4 inhibits histone H3 and tubulin acetylation at 0.1 μM concentration, blocks hyperphosphorylation of tau protein, and shows interesting immunomodulatory and neuroprotective properties. These features, together with its ability to cross the blood-brain barrier and its favorable physical-chemical properties, make compound 4 a promising hit for the development of innovative disease-modifying agents.

Impact of GSK-3β and CK-1δ on Wnt signaling pathway in alzheimer disease: A dual target approach

Alzheimer's disease (AD) is an enigmatic neurological illness that offers few treatment options. Recent exploration has highlighted the crucial connection of the Wnt signaling pathway in AD pathogenesis, shedding light on potential therapeutic targets. The present study focuses on the dual targeting of glycogen synthase kinase-3β (GSK-3β) and casein kinase-1δ (CK-1δ) within the framework of the Wnt signaling pathway as a possible technique for AD intervention. GSK-3β and CK-1δ are multifunctional kinases known for their roles in tau hyperphosphorylation, amyloid processing, and synaptic dysfunction, all of which are major hallmarks of Alzheimer's disease. They are intricately linked to Wnt signaling, which plays a pivotal part in sustaining neuronal function and synaptic plasticity. Dysregulation of the Wnt pathway in AD contributes to cognitive decline and neurodegeneration. This review delves into the molecular mechanisms by which GSK-3β and CK-1δ impact the Wnt signaling pathway, elucidating their roles in AD pathogenesis. We discuss the potential of small-molecule inhibitors along with their SAR studies along with the multi-targetd approach targeting GSK-3β and CK-1δ to modulate Wnt signaling and mitigate AD-related pathology. In summary, the dual targeting of GSK-3β and CK-1δ within the framework of the Wnt signaling pathway presents an innovative and promising avenue for future AD therapies, offering new hope for patients and caregivers in the quest to combat this challenging condition.

Reduction of Amyloid-β Production without Inhibiting Secretase Activity by MS-275

Brain amyloid-β (Aβ) governs the pathogenic process of Alzheimer's disease. Clinical trials to assess the disease-modifying effects of inhibitors or modulators of β- and γ-secretases have not shown clinical benefit and can cause serious adverse events. Previously, we found that the interleukin-like epithelial-to-mesenchymal transition inducer (ILEI, also known as FAM3C) negatively regulates the Aβ production through a decrease in Aβ immediate precursor, without the inhibition of β- and γ-secretase activity. Herein, we found that MS-275, a benzamide derivative that is known to inhibit histone deacetylases (HDACs), exhibits ILEI-like activity to reduce Aβ production independent of HDAC inhibition. Chronic MS-275 treatment decreased Aβ deposition in the cerebral cortex and hippocampus in an Alzheimer's disease mouse model. Overall, our results indicate that MS-275 is a potential therapeutic candidate for efficiently reducing brain Aβ accumulation.

Alzheimer's Disease-Related Epigenetic Changes: Novel Therapeutic Targets

Aging is a significant risk factor for Alzheimer's disease (AD), although the precise mechanism and molecular basis of AD are not yet fully understood. Epigenetic mechanisms, such as DNA methylation and hydroxymethylation, mitochondrial DNA methylation, histone modifications, and non-coding RNAs (ncRNAs), play a role in regulating gene expression related to neuron plasticity and integrity, which are closely associated with learning and memory development. This review describes the impact of dynamic and reversible epigenetic modifications and factors on memory and plasticity throughout life, emphasizing their potential as target for therapeutic intervention in AD. Additionally, we present insight from postmortem and animal studies on abnormal epigenetics regulation in AD, as well as current strategies aiming at targeting these factors in the context of AD therapy.

Histone deacetylase inhibitors VPA and WT161 ameliorate the pathological features and cognitive impairments of the APP/PS1 Alzheimer's disease mouse model by regulating the expression of APP secretases

BACKGROUND

Alzheimer's disease (AD) is a degenerative neurological disorder. Recent studies have indicated that histone deacetylases (HDACs) are among the most prominent epigenetic therapy targets and that HDAC inhibitors have therapeutic effects on AD. Here, we identified sodium valproate (VPA), a pan-HDAC inhibitor, and WT161, a novel HDAC6 selective inhibitor, as potential therapeutic agents for AD. Underlying molecular mechanisms were investigated.

METHODS

A cellular model, N2a-APPswe, was established via lentiviral infection, and the APPswe/PSEN1dE9 transgenic mouse model was employed in the study. LC-MS/MS was applied to quantify the concentration of WT161 in the mouse brain. Western blotting, immunohistochemical staining, thioflavin-S staining and ELISA were applied to detect protein expression in cells, tissues, or serum. RNA interference was utilized to knockdown the expression of specific genes in cells. The cognitive function of mice was assessed via the nest-building test, novel object recognition test and Morris water maze test.

RESULTS

Previous studies have focused mainly on the impact of HDAC inhibitors on histone deacetylase activity. Our study discovered that VPA and WT161 can downregulate the expression of multiple HDACs, such as HDAC1 and HDAC6, in both AD cell and mouse models. Moreover, they also affect the expression of APP and APP secretases (BACE1, PSEN1, ADAM10). RNA interference and subsequent vitamin C induction further confirmed that the expression of APP and APP secretases is indeed regulated by HDAC1 and HDAC6, with the JNK pathway being the intermediate link in this regulatory process. Through the above pathways, VPA and WT161 effectively reduced Aβ deposition in both AD cell and mouse models and significantly improved cognitive function in AD mice.

CONCLUSIONS

In general, we have discovered that the HDAC6-JNK-APP secretases cascade is an important pathway for VPA and WT161 to exert their therapeutic effects on AD. Investigations into the safety and efficacy of VPA and WT161 were also conducted, providing essential preclinical evidence for assessing these two epigenetic drugs for the treatment of AD.

Activation of β2-adrenergic receptors prevents AD-type synaptotoxicity via epigenetic mechanisms

We previously reported that prolonged exposure to an enriched environment (EE) enhances hippocampal synaptic plasticity, with one of the significant mechanistic pathways being activation of β2-adrenergic receptor (β2-AR) signaling, thereby mitigating the synaptotoxic effects of soluble oligomers of amyloid β-protein (oAβ). However, the detailed mechanism remained elusive. In this work, we recorded field excitatory postsynaptic potentials (fEPSP) in the CA1 region of mouse hippocampal slices treated with or without toxic Aβ-species. We found that pharmacological activation of β2-AR, but not β1-AR, selectively mimicked the effects of EE in enhancing LTP and preventing oAβ-induced synaptic dysfunction. Mechanistic analyses showed that certain histone deacetylase (HDAC) inhibitors mimicked the benefits of EE, but this was not seen in β2-AR knockout mice, suggesting that activating β2-AR prevents oAβ-mediated synaptic dysfunction via changes in histone acetylation. EE or activation of β-ARs each decreased HDAC2, whereas Aβ oligomers increased HDAC2 levels in the hippocampus. Further, oAβ-induced inflammatory effects and neurite degeneration were prevented by either β2-AR agonists or certain specific HDAC inhibitors. These preclinical results suggest that activation of β2-AR is a novel potential therapeutic strategy to mitigate oAβ-mediated features of AD.

The Contribution of Hippocampal All-Trans Retinoic Acid (ATRA) Deficiency to Alzheimer's Disease: A Narrative Overview of ATRA-Dependent Gene Expression in Post-Mortem Hippocampal Tissue

There is accumulating evidence that vitamin A (VA) deficiency contributes to the pathogenesis and progression of Alzheimer's disease (AD). All-trans retinoic acid (ATRA), a metabolite of VA in the brain, serves distinct roles in the human hippocampus. Agonists of retinoic acid receptors (RAR), including ATRA, promote activation of the non-amyloidogenic pathway by enhancing expression of α-secretases, providing a mechanistic basis for delaying/preventing amyloid beta (Aβ) toxicity. However, whether ATRA is actually deficient in the hippocampi of patients with AD is not clear. Here, using a publicly available human transcriptomic dataset, we evaluated the extent to which ATRA-sensitive genes are dysregulated in hippocampal tissue from post-mortem AD brains, relative to age-matched controls. Consistent with ATRA deficiency, we found significant dysregulation of many ATRA-sensitive genes and significant upregulation of RAR co-repressors, supporting the idea of transcriptional repression of ATRA-mediated signaling. Consistent with oxidative stress and neuroinflammation, Nrf2 and NfkB transcripts were upregulated, respectively. Interestingly, transcriptional targets of Nrf2 were not upregulated, accompanied by upregulation of several histone deacetylases. Overall, our investigation of ATRA-sensitive genes in the human hippocampus bolsters the scientific premise of ATRA depletion in AD and that epigenetic factors should be considered and addressed as part of VA supplementation.

Selective HDAC3 Inhibitors with Potent In Vivo Antitumor Efficacy against Triple-Negative Breast Cancer

HDAC3 modulation shows promise for breast cancer, including triple-negative cases. Novel pyrazino-hydrazide-based HDAC3 inhibitors were designed and synthesized. Lead compound 4i exhibited potent HDAC3 inhibition (IC50 = 14 nM) with at least 121-fold selectivity. It demonstrated strong cytotoxicity against triple-negative breast cancer cells (IC50: 0.55 μM for 4T1, 0.74 μM for MDA-MB-231) with least normal cell toxicity. Metabolically stable 4i displayed a superior pharmacokinetic profile. A dose-dependent therapeutic efficacy of 4i was observed in a tumor-bearing mouse model. The biomarker analysis with tumor tissues displayed enhanced acetylation on Ac-H3K9, Ac-H3K27, and Ac-H4K12 compared to Ac-tubulin and Ac-SMC3 indicating HDAC3 selectivity of 4i in vivo. The immunoblotting study with tumor tissue showed upregulation of apoptotic proteins caspase-3, caspase-7, and cytochrome c and the downregulation of proliferation markers Bcl-2, CD44, EGFR, and Ki-67. Compound 4i represents a promising candidate for targeted breast cancer therapy, particularly for cases with triple-negative breast cancer.

Design, synthesis, and biological evaluation of novel N-Benzyl piperidine derivatives as potent HDAC/AChE inhibitors for Alzheimer's disease

The multitarget-directed ligands approach represents a potential strategy to provide effective treatments for Alzheimer's disease (AD) given its multifactorial pathology. Herein, a series of N-benzyl piperidine derivatives were designed, synthesized, and biologically characterized for dual inhibitions of histone deacetylase (HDAC) and acetylcholinesterase (AChE). Among the compounds tested, d5 and d10 exhibited dual enzyme inhibitions (d5: HDAC_IC50 = 0.17 μM, AChE_IC50 = 6.89 μM, d10: HDAC_IC50 = 0.45 μM, AChE_IC50 = 3.22 μM), and both compounds showed activities on scavenging free radical, metal chelating, and inhibiting Aβ aggregations. More importantly, both compounds exhibited promising neuroprotective activities in PC-12 cells and good AChE selectivity. Collectively, the multifunctional profiles of compound d5 and d10 encourage further optimization and exploration to develop more potent analogues as potential treatments for AD.

Hydroxypyrone derivatives in drug discovery: from chelation therapy to rational design of metalloenzyme inhibitors

The versatile structural motif of hydroxypyrone is found in natural products and can be easily converted into hydroxypyridone and hydroxythiopyridone analogues. The favourable toxicity profile and ease of functionalization to access a vast library of compounds make them an ideal structural scaffold for drug design and discovery. This versatile scaffold possesses excellent metal chelating properties that can be exploited for chelation therapy in clinics. Deferiprone [1,2-dimethyl-3-hydroxy-4(1H)-one] was the first orally active chelator to treat iron overload in thalassemia major. Metal complexes of hydroxy-(thio)pyr(id)ones have been investigated as magnetic resonance imaging contrast agents, and anticancer and antidiabetic agents. In recent years, this compound class has demonstrated potential in discovering and developing metalloenzyme inhibitors. This review article summarizes recent literature on hydroxy-(thio)pyr(id)ones as inhibitors for metalloenzymes such as histone deacetylases, tyrosinase and metallo-β-lactamase. Different approaches to the design of hydroxy-(thio)pyr(id)ones and their biological properties against selected metalloenzymes are discussed.

Characterizing HDAC Pathway Copy Number Variation in Pan-Cancer

Background: Histone deacetylase (HDAC) plays a crucial role in regulating the expression and activity of a variety of genes associated with tumor progression and immunotherapeutic processes. The aim of this study was to characterize HDAC pathway copy number variation (CNV) in pan-cancer. Methods: A total of 10,678 tumor samples involving 33 types of tumors from The Cancer Genome Atlas (TCGA) were included in the study. Results: HDAC pathway CNV and CNV gain were identified as prognostic risk factors for pan-cancer species. The differences of tumor characteristics including tumor mutational burden, tumor neoantigen burden, high-microsatellite instability, and microsatellite stable between HDAC pathway CNV altered-type group and wild-type group varied among the various cancer species. In some cancer types, HDAC pathway CNV alteration was positively correlated with loss of heterozygosity, CNV burden, ploidy, and homologous recombination defect score markers, while it was significantly negatively correlated with immune score and stroma score. There were significant differences in immune characteristics such as major histocompatibility complex class I (MHC-I), MHC-II, chemokines, cytolytic-activity, and IFN-γ between the two groups. Immune cycle characteristics varied from one cancer type to another. Conclusion: This study reveals a tumor and immune profile of HDAC pathway CNV as well as its unlimited potential in immune prognosis.

Role of Histone Post-Translational Modifications in Inflammatory Diseases

Inflammation is a defensive reaction for external stimuli to the human body and generally accompanied by immune responses, which is associated with multiple diseases such as atherosclerosis, type 2 diabetes, Alzheimer’s disease, psoriasis, asthma, chronic lung diseases, inflammatory bowel disease, and multiple virus-associated diseases. Epigenetic mechanisms have been demonstrated to play a key role in the regulation of inflammation. Common epigenetic regulations are DNA methylation, histone modifications, and non-coding RNA expression; among these, histone modifications embrace various post-modifications including acetylation, methylation, phosphorylation, ubiquitination, and ADP ribosylation. This review focuses on the significant role of histone modifications in the progression of inflammatory diseases, providing the potential target for clinical therapy of inflammation-associated diseases.

Prevention of anticancer therapy-induced neurotoxicity: putting DNA damage in perspective

Chemotherapy-induced peripheral neuropathy (CIPN) is a severe side effect of conventional cancer therapeutics (cAT) that significantly impacts the quality of life of tumor patients. The molecular mechanisms of CIPN are incompletely understood and there are no effective preventive or therapeutic measures available to date. Here, we present a brief overview of the current knowledge about mechanisms underlying CIPN and discuss DNA damage-related stress responses as feasible targets for the prevention of CIPN. In addition, we discuss that the nematode Caenorhabditis elegans is a useful 3R-conform model organism to further elucidate molecular mechanisms of CIPN and to identify novel lead compounds protecting from cAT-triggered neuropathy.

Degradation and inhibition of epigenetic regulatory protein BRD4 exacerbate Alzheimer's disease-related neuropathology in cell models

Epigenetic regulation plays substantial roles in human pathophysiology, which provides opportunities for intervention in human disorders through the targeting of epigenetic pathways. Recently, emerging evidence from preclinical studies suggested the potential in developing therapeutics of Alzheimer's disease (AD) by targeting bromodomain containing protein 4 (BRD4), an epigenetic regulatory protein. However, further characterization of AD-related pathological events is urgently required. Here, we investigated the effects of pharmacological degradation or inhibition of BRD4 on AD cell models. Interestingly, we found that both degradation and inhibition of BRD4 by ARV-825 and JQ1, respectively, robustly increased the levels of amyloid-beta (Aβ), which has been associated with the neuropathology of AD. Subsequently, we characterized the mechanisms by which downregulation of BRD4 increases Aβ levels. We found that both degradation and inhibition of BRD4 increased the levels of BACE1, the enzyme responsible for cleavage of the amyloid-beta protein precursor (APP) to generate Aβ. Consistent with Aβ increase, we also found that downregulation of BRD4 increased AD-related phosphorylated Tau (pTau) protein in our 3D-AD human neural cell culture model. Therefore, our results suggest that downregulation of BRD4 would not be a viable strategy for AD intervention. Collectively, our study not only shows that BRD4 is a novel epigenetic component that regulates BACE1 and Aβ levels, but also provides novel and translational insights into the targeting of BRD4 for potential clinical applications.

Development of a Novel, Small-Molecule Brain-Penetrant Histone Deacetylase Inhibitor That Enhances Spatial Memory Formation in Mice

Histone acetylation is a prominent epigenetic modification linked to the memory loss symptoms associated with neurodegenerative disease. The use of existing histone deacetylase inhibitor (HDACi) drugs for treatment is precluded by their weak blood-brain barrier (BBB) permeability and undesirable toxicity. Here, we address these shortcomings by developing a new class of disulfide-based compounds, inspired by the scaffold of the FDA-approved HDACi romidepsin (FK288). Our findings indicate that our novel compound MJM-1 increases the overall level of histone 3 (H3) acetylation in a prostate cancer cell line. In mice, MJM-1 injected intraperitoneally (i.p.) crossed the BBB and could be detected in the hippocampus, a brain region that mediates memory. Consistent with this finding, we found that the post-training i.p. administration of MJM-1 enhanced hippocampus-dependent spatial memory consolidation in male mice. Therefore, MJM-1 represents a potential lead for further optimization as a therapeutic strategy for ameliorating cognitive deficits in aging and neurodegenerative diseases.

Inhibitory activities of grape bioactive compounds against enzymes linked with human diseases

A quest for identification of novel, safe and efficient natural compounds, as additives in the modern food and cosmetic industries, has been prompted by concerns about toxicity and side effects of synthetic products. Plant phenolic compounds are one of the most documented natural products due to their multifarious biological applications. Grape (Vitis vinifera) is an important source of phenolic compounds such as phenolic acids, tannins, quinones, coumarins and, most importantly, flavonoids/flavones. This review crisply encapsulates enzyme inhibitory activities of various grape polyphenols towards different key human-ailment-associated enzymes: xanthine oxidase (gout), tyrosinase (hyperpigmentation), α-amylase and α-glucosidase (diabetes mellitus), pancreatic lipase (obesity), cholinesterase (Alzheimer's disease), angiotensin i-converting enzymes (hypertension), α-synuclein (Parkinson's disease) and histone deacetylase (various diseases). The review also depicts the enzyme inhibitory mechanism of various grape polyphenols and briefly discusses their stature as potential therapeutic and drug development candidates. KEY POINTS: • Nineteen major bioactive polyphenols from the grape/grape products and their disease targets are presented • Sixty-two important polyphenols as enzyme inhibitors from grape/grape products are presented • A thorough description and graphical presentation of biological significance of polyphenols against various diseases.

Therapeutic potential of quinazoline derivatives for Alzheimer's disease: A comprehensive review

Quinazolines are considered as a promising class of bioactive heterocyclic compounds with broad properties. Particularly, the quinazoline scaffold has an impressive role in the design and synthesis of new CNS-active drugs. The drug-like properties and pharmacological characteristics of quinazoline could lead to different drugs with various targets. Among CNS disorders, Alzheimer's disease (AD) is a progressive neurodegenerative disorder with memory loss, cognitive decline and language dysfunction. AD is a complex and multifactorial disease therefore, the need for finding multi-target drugs against this devastative disease is urgent. A literature survey revealed that quinazoline derivatives have diverse therapeutic potential for AD as modulators/inhibitors of β-amyloid, tau protein, cholinesterases, monoamine oxidases, and phosphodiesterases as well as other protective effects. Thus, we describe here the most relevant and recent studies about anti-AD agents with quinazoline structure which can further aid the development and discovery of new anti-AD agents.

Polypharmacology: The science of multi-targeting molecules

Polypharmacology is a concept where a molecule can interact with two or more targets simultaneously. It offers many advantages as compared to the conventional single-targeting molecules. A multi-targeting drug is much more efficacious due to its cumulative efficacy at all of its individual targets making it much more effective in complex and multifactorial diseases like cancer, where multiple proteins and pathways are involved in the onset and development of the disease. For a molecule to be polypharmacologic in nature, it needs to possess promiscuity which is the ability to interact with multiple targets; and at the same time avoid binding to antitargets which would otherwise result in off-target adverse effects. There are certain structural features and physicochemical properties which when present would help researchers to predict if the designed molecule would possess promiscuity or not. Promiscuity can also be identified via advanced state-of-the-art computational methods. In this review, we also elaborate on the methods by which one can intentionally incorporate promiscuity in their molecules and make them polypharmacologic. The polypharmacology paradigm of "one drug-multiple targets" has numerous applications especially in drug repurposing where an already established drug is redeveloped for a new indication. Though designing a polypharmacological drug is much more difficult than designing a single-targeting drug, with the current technologies and information regarding different diseases and chemical functional groups, it is plausible for researchers to intentionally design a polypharmacological drug and unlock its advantages.

Cashew Nut Shell Liquid (CNSL) as a Source of Drugs for Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder with a multifaceted pathogenesis. This fact has long halted the development of effective anti-AD drugs. Recently, a therapeutic strategy based on the exploitation of Brazilian biodiversity was set with the aim of discovering new disease-modifying and safe drugs for AD. In this review, we will illustrate our efforts in developing new molecules derived from Brazilian cashew nut shell liquid (CNSL), a natural oil and a byproduct of cashew nut food processing, with a high content of phenolic lipids. The rational modification of their structures has emerged as a successful medicinal chemistry approach to the development of novel anti-AD lead candidates. The biological profile of the newly developed CNSL derivatives towards validated AD targets will be discussed together with the role of these molecular targets in the context of AD pathogenesis.

Histone deacetylase in neuropathology

Neuroepigenetics, a new branch of epigenetics, plays an important role in the regulation of gene expression. Neuroepigenetics is associated with holistic neuronal function and helps in formation and maintenance of memory and learning processes. This includes neurodevelopment and neurodegenerative defects in which histone modification enzymes appear to play a crucial role. These modifications, carried out by acetyltransferases and deacetylases, regulate biologic and cellular processes such as apoptosis and autophagy, inflammatory response, mitochondrial dysfunction, cell-cycle progression and oxidative stress. Alterations in acetylation status of histone as well as non-histone substrates lead to transcriptional deregulation. Histone deacetylase decreases acetylation status and causes transcriptional repression of regulatory genes involved in neural plasticity, synaptogenesis, synaptic and neural plasticity, cognition and memory, and neural differentiation. Transcriptional deactivation in the brain results in development of neurodevelopmental and neurodegenerative disorders. Mounting evidence implicates histone deacetylase inhibitors as potential therapeutic targets to combat neurologic disorders. Recent studies have targeted naturally-occurring biomolecules and micro-RNAs to improve cognitive defects and memory. Multi-target drug ligands targeting HDAC have been developed and used in cell-culture and animal-models of neurologic disorders to ameliorate synaptic and cognitive dysfunction. Herein, we focus on the implications of histone deacetylase enzymes in neuropathology, their regulation of brain function and plausible involvement in the pathogenesis of neurologic defects.

Understanding the role of histone deacetylase and their inhibitors in neurodegenerative disorders: Current targets and future perspective

Neurodegenerative diseases are a group of pathological conditions that cause motor inc-ordination (jerking movements), cognitive and memory impairments result from degeneration of neurons in a specific area of the brain. Oxidative stress, mitochondrial dysfunction, excitotoxicity, neuroinflammation, neurochemical imbalance and histone deacetylase enzymes (HDAC) are known to play a crucial role in neurodegeneration. HDAC is classified into four categories (class I, II, III and class IV) depending upon their location and functions. HDAC1 and 2 are involved in neurodegeneration, while HDAC3-11 and class III HDACs are beneficial as neuroprotective. HDACs are localized in different parts of the brain- HDAC1 (hippocampus and cortex), HDAC2 (nucleus), HDAC3, 4, 5, 7 and 9 (nucleus and cytoplasm), HDAC6 & HDAC7 (cytoplasm) and HDAC11 (Nucleus, cornus ammonis 1 and spinal cord). In pathological conditions, HDAC up-regulates glutamate, phosphorylation of tau, and glial fibrillary acidic proteins while down-regulating BDNF, Heat shock protein 70 and Gelsolin. Class III HDACs are divided into seven sub-classes (SIRT1-SIRT7). Sirtuins are localized in the different parts of the brain and neuron -Sirt1 (nucleus), Sirt2 (cortex, striatum, hippocampus and spinal cord), Sirt3 (mitochondria and cytoplasm), Sirt4, Sirt5 & Sirt6 (mitochondria), Sirt7 (nucleus) and Sirt8 (nucleolus). SIRTs (1, 3, 4, and 6) are involved in neuronal survival, proliferation and modulating stress response, and SIRT2 is associated with Parkinsonism, Huntington’s disease and Alzheimer’s disease, whereas SIRT6 is only associated with Alzheimer’s disease. In this critical review, we have discussed the mechanisms and therapeutic targets of HDACs that would be beneficial for the management of neurodegenerative disorders.

Personalizing the Care and Treatment of Alzheimer's Disease: An Overview

Alzheimer's disease (AD) is a progressive, complex, and multifactorial neurodegenerative disorder, still without effective and stable therapeutic strategies. Currently, available medications for AD are based on symptomatic therapy, which include acetylcholinesterase (AChE) inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonist. Additionally, medications such as antipsychotic drugs, antidepressants, sedative, and hypnotic agents, and mood stabilizers are used for the management of behavioral and psychological symptoms of dementia (BPSD). Clinical research has been extensively investigated treatments focusing on the hallmark pathology of AD, including the amyloid deposition, tau hyperphosphorylation, neuroinflammation, and vascular changes; however, so far without success, as all new potential drugs failed to show significant clinical benefit. The underlying heterogeneous etiology and diverse symptoms of AD suggest that a precision medicine strategy is required, which would take into account the complex genetic, epigenetic, and environmental landscape of each AD patient. The article provides a comprehensive overview of the literature on AD, the current and potential therapy of both cognitive symptoms as well as BPSD, with a special focus on gut microbiota and epigenetic modifications as new emerging drug targets. Their specific patterns could represent the basis for novel individually tailored approaches aimed to optimize precision medicine strategies for AD prevention and treatment. However, the successful application of precision medicine to AD demands a further extensive research of underlying pathological processes, as well as clinical and biological complexity of this multifactorial neurodegenerative disorder.

Histone deacetylase 3 in hippocampus contributes to memory impairment after chronic constriction injury of sciatic nerve in mice

ABSTRACT

Chronic neuropathic pain is frequently accompanied by memory impairment, yet the underlying mechanisms remain unclear. Here, we showed that mice displayed memory impairment starting at 14 days and lasting for at least 21 days after chronic constriction injury (CCI) of unilateral sciatic nerve in mice. Systemic administration of the pan histone deacetylase (HDAC) inhibitor sodium butyrate attenuated this memory impairment. More specifically, we found that hippocampus HDAC3 was involved in this process because the levels of its mRNA and protein increased significantly in the hippocampus at 14 and 21 days after CCI, but not sham surgery. Systemic administration of the selective HDAC3 antagonist RGFP966 attenuated CCI-induced memory impairment, improved hippocampal long-term potentiation impairment, and rescued reductions of dendritic spine density and synaptic plasticity-associated protein in the hippocampus. In addition, HDAC3 overexpression in the hippocampus led to memory impairment without affecting basal nociceptive responses in naive mice. Our findings suggest that HDAC3 contributes to memory impairment after CCI by impairing synaptic plasticity in hippocampus. Histone deacetylase 3 might serve as a potential molecular target for therapeutic treatment of memory impairment under neuropathic pain conditions.

Melatonin- and Ferulic Acid-Based HDAC6 Selective Inhibitors Exhibit Pronounced Immunomodulatory Effects In Vitro and Neuroprotective Effects in a Pharmacological Alzheimer's Disease Mouse Model

The structures of melatonin and ferulic acid were merged into tertiary amide-based histone deacetylase 6 (HDAC6) inhibitors to develop multi-target-directed inhibitors for neurodegenerative diseases to incorporate antioxidant effects without losing affinity and selectivity at HDAC6. Structure-activity relationships led to compound 10b as a hybrid molecule showing pronounced and selective inhibition of HDAC6 (IC50 = 30.7 nM, > 25-fold selectivity over other subtypes). This compound shows comparable DPPH radical scavenging ability to ferulic acid, comparable ORAC value to melatonin and comparable Cu²⁺ chelating ability to EDTA. It also lacks neurotoxicity on HT-22 cells, exhibits a pronounced immunomodulatory effect, and is active in vivo showing significantly higher efficacy in an AD mouse model to prevent both Aβ25-35-induced spatial working and long-term memory dysfunction at lower dose (0.3 mg/kg) compared to positive control HDAC6 inhibitor ACY1215 and an equimolar mixture of the three entities ACY1215, melatonin and ferulic acid, suggesting potentially disease-modifying properties.

Quantitative proteomics of epigenetic histone modifications in MCF-7 cells under estradiol stimulation

Estrogen exposure has already been considered to be associated with tumorigenesis and breast cancer progression. To study the epigenetic regulation mechanism in MCF-7 cells under estrogen exposure, which normally results in cell proliferation and malignancy, a stable isotope labeling of amino acid (SILAC) based quantitative proteomics strategy was used to analyse histone post-translational modifications (PTMs) and protein differential expressions. In total, we have unambiguously identified 49 histone variants and quantified 42 of them, in which two differentially expressed proteins were found to be associated with breast cancers. Through the quantitative analysis of 470 histone peptides with a combination of different PTM types, including methylation (mono-, di-, and tri-), acetylation and phosphorylation, 150 of them were found to be differentially expressed. Through the biological analysis of the quantification results of both histone PTMs and proteins in MCF-7 cells, we found that (1) the histone variants H10 and H2AV have an effect on the adjustment of the nucleosome or chromatin structure and activate target genes; (2) after estrogen receptor (ER) activation by estrogen, the recruitment of histone acetyltransferase KAT7 might affect the acetylation at the N terminal of H4 (K5, K8 and K12) and also result in cross-talk between different acetylation sites; (3) different expression of histone deacetylase HDAC2 and its nucleo-cytoplasmic transportation process is important in the regulation of histone acetylation in MCF-7 cells under estrogen exposure.

Epigenetic Regulation of Amyloid-beta Metabolism in Alzheimer's Disease

Senile plaques (SPs) are one of the pathological features of Alzheimer's disease (AD) and they are formed by the overproduction and aggregation of amyloid-beta (Aβ) peptides derived from the abnormal cleavage of amyloid precursor protein (APP). Thus, understanding the regulatory mechanisms during Aβ metabolism is of great importance to elucidate AD pathogenesis. Recent studies have shown that epigenetic modulation-including DNA methylation, non-coding RNA alterations, and histone modifications-is of great significance in regulating Aβ metabolism. In this article, we review the aberrant epigenetic regulation of Aβ metabolism.

Age-Related Macular Degeneration: From Epigenetics to Therapeutic Implications

Aberrant regulation of epigenetic mechanisms, including the two most common types; DNA methylation and histone modification have been implicated in common chronic progressive conditions, including Alzheimer disease, cardiovascular disease, and age-related macular degeneration (AMD). All these conditions are complex, meaning that environmental factors, genetic factors, and their interactions play a role in disease pathophysiology. Although genome wide association studies (GWAS), and studies on twins demonstrate the genetic/hereditary component to these complex diseases, including AMD, this contribution is much less than 100%. Moreover, the contribution of the hereditary component decreases in the advanced, later onset forms of these chronic diseases including AMD. This underscores the need to elucidate how the genetic and environmental factors function to exert their influence on disease pathophysiology. By teasing out epigenetic mechanisms and how they exert their influence on AMD, therapeutic targets can be tailored to prevent and/or slow down disease progression. Epigenetic studies that incorporate well-characterized patient tissue samples (including affected tissues and peripheral blood), similar to those relevant to gene expression studies, along with genetic and epidemiological information, can be the first step in developing appropriate functional assays to validate findings and identify potential therapies.

HDAC6 in Diseases of Cognition and of Neurons

Central nervous system (CNS) neurodegenerative diseases are characterized by faulty intracellular transport, cognition, and aggregate regulation. Traditionally, neuroprotection exerted by histone deacetylase (HDAC) inhibitors (HDACi) has been attributed to the ability of this drug class to promote histone acetylation. However, HDAC6 in the healthy CNS functions via distinct mechanisms, due largely to its cytoplasmic localization. Indeed, in healthy neurons, cytoplasmic HDAC6 regulates the acetylation of a variety of non-histone proteins that are linked to separate functions, i.e., intracellular transport, neurotransmitter release, and aggregate formation. These three HDAC6 activities could work independently or in synergy. Of particular interest, HDAC6 targets the synaptic protein Bruchpilot and neurotransmitter release. In pathological conditions, HDAC6 becomes abundant in the nucleus, with deleterious consequences for transcription regulation and synapses. Thus, HDAC6 plays a leading role in neuronal health or dysfunction. Here, we review recent findings and novel conclusions on the role of HDAC6 in neurodegeneration. Selective studies with pan-HDACi are also included. We propose that an early alteration of HDAC6 undermines synaptic transmission, while altering transport and aggregation, eventually leading to neurodegeneration.

Glycogen Synthase Kinase 3β: A New Gold Rush in Anti-Alzheimer's Disease Multitarget Drug Discovery?

Alzheimer’s disease (AD), like other multifactorial diseases, is the result of a systemic breakdown of different physiological networks. As result, several lines of evidence suggest that it could be more efficiently tackled by molecules directed toward different dysregulated biochemical targets or pathways. In this context, the selection of targets to which the new molecules will be directed is crucial. For years, the design of such multitarget-directed ligands (MTDLs) has been based on the selection of main targets involved in the “cholinergic” and the “β-amyloid” hypothesis. Recently, there have been some reports on MTDLs targeting the glycogen synthase kinase 3β (GSK-3β) enzyme, due to its appealing properties. Indeed, this enzyme is involved in tau hyperphosphorylation, controls a multitude of CNS-specific signaling pathways, and establishes strict connections with several factors implicated in AD pathogenesis. In the present Miniperspective, we will discuss the reasons behind the development of GSK-3β-directed MTDLs and highlight some of the recent efforts to obtain these new classes of MTDLs as potential disease-modifying agents.

The glial-specific hypermethylated 3' untranslated region of histone deacetylase 1 may modulates several signal pathways in Alzheimer's disease

AIMS

Epigenetic regulation plays an important role in the progression of Alzheimer's disease (AD). Here, we identified differential methylation probes (DMP) and investigated their potential mechanistic roles in AD.

MAIN METHODS

DMPs were identified via bioinformatic analysis of GSE66351, which was made up with 106 AD samples and 84 control samples derived from three separate brain regions. Differentially expressed genes (DEGs) were analyzed based on GSE5281 comprising 45 control samples and 58 AD samples. Gene ontology (GO), gene set enrichment analysis (GSEA), and protein-protein interaction (PPI) were used to identify pathways and hub genes.

KEY FINDINGS

We found 9007 DMPs in Occipital Cortex glia, 1527 in OC neurons, 100 in Temporal Cortex, and 194 in Frontal Cortex. 74 DEGs were identified in Primary Visual Cortex, 67 of which were downregulated while seven upregulated. 482 were upregulated and 697 downregulated in medial temporal gyrus. In superior frontal gyrus, 687 were upregulated and 85 downregulated. GO and PPI revealed that pathways involving epithelial-cell differentiation, cellular responses to lipids, transcription corepressor activities, apoptotic and organ growth were modulated by histone deacetylase 1 (HDAC1) and associated with AD. Additionally, GSEA illustrated that the transforming growth factor beta signaling pathway was significantly enriched in some brain regions and HDAC1 played an important role in this pathway.

SIGNIFICANCE

We found the glial-specific 3'UTR of HDAC1 was hypermethylated and HDAC1 was overexpressed in AD patients. Moreover, we also speculate that HDAC1 triggered signaling pathways linked to many different biological processes and functions via the regulation of histone deacetylation.

An up-to-date overview of computational polypharmacology in modern drug discovery

INTRODUCTION

In recent years, computational polypharmacology has gained significant attention to study the promiscuous nature of drugs. Despite tremendous challenges, community-wide efforts have led to a variety of novel approaches for predicting drug polypharmacology. In particular, some rapid advances using machine learning and artificial intelligence have been reported with great success.

AREAS COVERED

In this article, the authors provide a comprehensive update on the current state-of-the-art polypharmacology approaches and their applications, focusing on those reports published after our 2017 review article. The authors particularly discuss some novel, groundbreaking concepts, and methods that have been developed recently and applied to drug polypharmacology studies.

EXPERT OPINION

Polypharmacology is evolving and novel concepts are being introduced to counter the current challenges in the field. However, major hurdles remain including incompleteness of high-quality experimental data, lack of in vitro and in vivo assays to characterize multi-targeting agents, shortage of robust computational methods, and challenges to identify the best target combinations and design effective multi-targeting agents. Fortunately, numerous national/international efforts including multi-omics and artificial intelligence initiatives as well as most recent collaborations on addressing the COVID-19 pandemic have shown significant promise to propel the field of polypharmacology forward.

Design and Synthesis of Dihydroxamic Acids as HDAC6/8/10 Inhibitors

We report the synthesis and evaluation of a class of selective multitarget agents for the inhibition of HDAC6, HDAC8, and HDAC10. The concept for this study grew out of a structural analysis of the two selective inhibitors Tubastatin A (HDAC6/10) and PCI-34051 (HDAC8), which we recognized share the same N-benzylindole core. Hybridization of the two inhibitor structures resulted in dihydroxamic acids with benzyl-indole and -indazole core motifs. These substances exhibit potent activity against HDAC6, HDAC8, and HDAC10, while retaining selectivity over HDAC1, HDAC2, and HDAC3. The best substance inhibited the viability of the SK-N-BE(2)C neuroblastoma cell line with an IC50 value similar to a combination treatment with Tubastatin A and PCI-34051. This compound class establishes a proof of concept for such hybrid molecules and could serve as a starting point for the further development of enhanced HDAC6/8/10 inhibitors.

In Vitro Assessment of the Genotoxic Hazard of Novel Hydroxamic Acid- and Benzamide-Type Histone Deacetylase Inhibitors (HDACi)

Histone deacetylase inhibitors (HDACi) are already approved for the therapy of leukemias. Since they are also emerging candidate compounds for the treatment of non-malignant diseases, HDACi with a wide therapeutic window and low hazard potential are desirable. Here, we investigated a panel of 12 novel hydroxamic acid- and benzamide-type HDACi employing non-malignant V79 hamster cells as toxicology guideline-conform in vitro model. HDACi causing a ≥10-fold preferential cytotoxicity in malignant neuroblastoma over non-malignant V79 cells were selected for further genotoxic hazard analysis, including vorinostat and entinostat for control. All HDACi selected, (i.e., KSK64, TOK77, DDK137 and MPK77) were clastogenic and evoked DNA strand breaks in non-malignant V79 cells as demonstrated by micronucleus and comet assays, histone H2AX foci formation analyses (γH2AX), DNA damage response (DDR) assays as well as employing DNA double-strand break (DSB) repair-defective VC8 hamster cells. Genetic instability induced by hydroxamic acid-type HDACi seems to be independent of bulky DNA adduct formation as concluded from the analysis of nucleotide excision repair (NER) deficient mutants. Summarizing, KSK64 revealed the highest genotoxic hazard and DDR stimulating potential, while TOK77 and MPK77 showed the lowest DNA damaging capacity. Therefore, these compounds are suggested as the most promising novel candidate HDACi for subsequent pre-clinical in vivo studies.

Histone deacetylase-3: Friend and foe of the brain

IMPACT STATEMENT

Brain development and degeneration are highly complex processes that are regulated by a large number of molecules and signaling pathways the identities of which are being unraveled. Accumulating evidence points to histone deacetylases and epigenetic mechanisms as being important regulators of these processes. In this review, we describe that histone deacetylase-3 (HDAC3) is a particularly crucial regulator of both neurodevelopment and neurodegeneration. In addition, HDAC3 regulates memory formation, synaptic plasticity, and the cognitive impairment associated with normal aging. Understanding how HDAC3 functions contributes to the normal development and functioning of the brain while also promoting neurodegeneration could lead to the development of therapeutic approaches for neurodevelopmental, neuropsychiatric, and neurodegenerative disorders.

Effect of C-phycocyanin on HDAC3 and miRNA-335 in Alzheimer's disease

BACKGROUND

Amyloid-beta (Aβ) plaque deposits and neurofibrillary tangles containing tau proteins are the key pathognomonic manifestations of Alzheimer's disease (AD). Lack of holistic drugs for AD has reinvigorated enthusiasm in the natural product-based therapies. In this study, our idea to decipher the beneficial effects of C-phycocyanin (CPC) in the management of AD is buoyed by its multifaceted and holistic therapeutic effects.

METHODS

We evaluated the effect of CPC treatment on epigenetic factors and inflammatory mediators in a mouse with oligomeric Aβ1-42-induced AD. Besides, the cognitive function was evaluated by the spatial memory performance on a radial arm maze.

RESULTS

The results showed cognitive deficit in the mice with AD along with upregulated HDAC3 expression and diminished miRNA-335 and brain-derived neurotrophic factor (BDNF) expressions. In addition, inflammation was provoked (manifested by increased interleukins (IL)-6 and IL-1β) and neuronal apoptosis was accelerated (indicated by increased Bax, caspase-3, and caspase-9 along with decreased Bcl2) in the hippocampus of the mice with AD. Interestingly, CPC treatment in the mice with AD improved spatial memory performance and decreased the perturbations in the epigenetic and inflammatory biofactors.

CONCLUSION

These results underscore that mitigation of inflammation via regulation of epigenetic factors might be the key pathway underlying the ameliorative effect of CPC against the aberrations in AD. Our findings provide the rationale for considering CPC as a viable therapeutic option in the management of AD.

Undiscovered Roles for Transthyretin: From a Transporter Protein to a New Therapeutic Target for Alzheimer's Disease

Transthyretin (TTR), an homotetrameric protein mainly synthesized by the liver and the choroid plexus, and secreted into the blood and the cerebrospinal fluid, respectively, has been specially acknowledged for its functions as a transporter protein of thyroxine and retinol (the latter through binding to the retinol-binding protein), in these fluids. Still, this protein has managed to stay in the spotlight as it has been assigned new and varied functions. In this review, we cover knowledge on novel TTR functions and the cellular pathways involved, spanning from neuroprotection to vascular events, while emphasizing its involvement in Alzheimer’s disease (AD). We describe details of TTR as an amyloid binding protein and discuss its interaction with the amyloid Aβ peptides, and the proposed mechanisms underlying TTR neuroprotection in AD. We also present the importance of translating advances in the knowledge of the TTR neuroprotective role into drug discovery strategies focused on TTR as a new target in AD therapeutics.

Histone deacetylases 1, 2 and 3 in nervous system development

Although histone acetylases (HDACS) were initially believed to render chromatin in a transcriptionally repressed state by deacetylating histones, it is now known that they both repress and activate transcription. Moreover, HDACs regulate the activity and/or function of a large number of other cellular proteins localized in the nucleus and cytoplasm. Accumulating evidence indicates that HDACs also play a key role in the development of the nervous system. This review focuses on three classical HDACS - HDACs 1, 2 and 3. Although much evidence on the involvement of HDACs in neurodevelopment has come from the use of pharmacological inhibitors, because these agents are not specific in their action on individual HDAC proteins, this review only describes evidence derived from the use of molecular genetic approaches. Our review describes that HDACs 1, 2 and 3 play crucial roles in neurodevelopment by regulating neurogenesis, gliogenesis, the development of neural circuitry and synaptic transmission.

Multitarget Approach for the Treatment of Alzheimer's Disease: Inhibition of Phosphodiesterase 9 (PDE9) and Histone Deacetylases (HDACs) Covering Diverse Selectivity Profiles

Here, we present a series of dual-target phosphodiesterase 9 (PDE9) and histone deacetylase (HDAC) inhibitors devised as pharmacological tool compounds for assessing the implications of these two targets in Alzheimer's disease (AD). These novel inhibitors were designed taking into account the key pharmacophoric features of known selective PDE9 inhibitors as well as privileged chemical structures, bearing zinc binding groups (hydroxamic acids and ortho-amino anilides) that hit HDAC targets. These substituents were selected according to rational criteria and previous knowledge from our group to explore diverse HDAC selectivity profiles (pan-HDAC, HDAC6 selective, and class I selective) that were confirmed in biochemical screens. Their functional response in inducing acetylation of histone and tubulin and phosphorylation of cAMP response element binding (CREB) was measured as a requisite for further progression into complete in vitro absorption, distribution, metabolism and excretion (ADME) and in vivo brain penetration profiling. Compound 31b, a selective HDAC6 inhibitor with acceptable brain permeability, was chosen for assessing in vivo efficacy of these first-in-class inhibitors, as well as studying their mode of action (MoA).

Taking Advantage of the Selectivity of Histone Deacetylases and Phosphodiesterase Inhibitors to Design Better Therapeutic Strategies to Treat Alzheimer's Disease

The discouraging results with therapies for Alzheimer’s disease (AD) in clinical trials, highlights the urgent need to adopt new approaches. Like other complex diseases, it is becoming clear that AD therapies should focus on the simultaneous modulation of several targets implicated in the disease. Recently, using reference compounds and the first-in class CM-414, we demonstrated that the simultaneous inhibition of histone deacetylases [class I histone deacetylases (HDACs) and HDAC6] and phosphodiesterase 5 (PDE5) has a synergistic therapeutic effect in AD models. To identify the best inhibitory balance of HDAC isoforms and PDEs that provides a safe and efficient therapy to combat AD, we tested the compound CM-695 in the Tg2576 mouse model of this disease. CM-695 selectively inhibits HDAC6 over class I HDAC isoforms, which largely overcomes the toxicity associated with HDAC class 1 inhibition. Furthermore, CM-695 inhibits PDE9, which is expressed strongly in the brain and has been proposed as a therapeutic target for AD. Chronic treatment of aged Tg2576 mice with CM-695 ameliorates memory impairment and diminishes brain Aβ, although its therapeutic effect was no longer apparent 4 weeks after the treatment was interrupted. An increase in the presence of 78-KDa glucose regulated protein (GRP78) and heat shock protein 70 (Hsp70) chaperones may underlie the therapeutic effect of CM-695. In summary, chronic treatment with CM-695 appears to reverse the AD phenotype in a safe and effective manner. Taking into account that AD is a multifactorial disorder, the multimodal action of these compounds and the different events they affect may open new avenues to combat AD.